1. Field of the Invention
The present invention relates to a method for continuous production of milk with a predetermined fat content. Whole milk is divided into a cream fraction and a skim milk fraction in a centrifugal separator. A part of the cream fraction is remixed into the skim milk fraction in order to obtain a mixed fraction of milk with a desired fat content.
2. Description of the Prior Art
The natural fat content of the milk varies with feeding and time of the year, but has usually an average value of about 4% fat. Consumer milk is usually for sale with a lower fat content 3,0, 1,5 or 0,5% fat. In smaller production scale it is possible to carry through the standardization in batches by dividing the whole milk into cream and skim milk in a centrifugal separator. Quantities of skim milk and cream which have been calculated in advance are led from the separator to a common collection vessel. After analysis of the fat content and a possible adjustment of the same the milk is packaged.
In modern dairies the standardization takes place as a continuous process by automatic direct standardization. In this process the whole milk is divided into two flows, cream and skim milk with constant fat contents in respective flow. In an "in-line"-system directly after the separator a controlled amount of cream is remixed with the skim milk in such a way that standardized milk with the desired fat content is obtained.
In the earliest processes for direct standardization the separator was provided with two manually operated control valves in the outlet for cream. One of the valves was connected to the outlet for skim milk and controlled the amount of cream which should be brought back to the skim milk. The second valve controlled the flow of surplus cream. The fat content in the cream was determined by how much the both valves were open altogether. The fat content of the standardized milk was determined by the fat content of the returned cream and the adjustment of the return valve. The adjustment of the position of the valves demanded skilled personnel. The exact fat content could be measured only by means of analysis at a laboratory.
In the processes for standardization which are used today in the dairies two control circuits are used. One circuit controls the flow of cream out from the separator. This circuit comprises flow meter for the cream flow, density transmitters which measure the fat content in the cream and a control valve arranged after the flow meter and the density transmitter. A second circuit controls the amount of cream which is remixed with the skim milk in order to give a standardized milk with a desired fat content. The flow of standardized milk is monitored as well as the flow of cream for remixing.
When using dairy processes in small scale on the farm the earlier method for standardization of fat makes too high demands on the personnel. The latter automatic method demands on the other hand too an expensive investment for a small scale production.